add examples

examples/BatteryMonitor/BatteryMonitor.ino

@@ -0,0 +1,25 @@
+#include <Battery.h>
+
+Battery battery(3400, 4200, A0);
+/**
+ * 1 cell li-ion/li-poly battery wired to A0 before voltage booster, on demand sensing on pin 3, linear mapping function
+ * https://github.com/rlogiacco/BatterySense#lesser-than-5v-with-voltage-booster
+ **/
+void setup() {
+	Serial.begin(9600);
+	while (!Serial);
+	battery.begin(5000, 1.0);
+}
+
+void loop() {
+	digitalWrite(13, HIGH);
+	delay(500);
+	digitalWrite(13, LOW);
+	delay(500);
+
+	Serial.print("Battery voltage is ");
+	Serial.print(battery.voltage());
+	Serial.print(" (");
+	Serial.print(battery.level());
+	Serial.println("%)");
+}